FIGS. 1 and 2 illustrate an IC structure disclosed in U.S. Pat. No. 5,702,255. The IC structure includes a cover 28, a BGA (ball grid array) package 12 having semiconductor elements provided therein, and a connector main body 24. From FIG. 2, it can be clearly seen that the BGA package 12 has ball-type contacts 20 that are connected to contact assemblies 26 provided on the connector main body 24. The contact assemblies 26 have ball-shaped lower ends that are in contact with terminal pads 14 provided on a circuit board 16. This is the so-called BGA type connection that is considered to be superior to the conventional SMT type connection.
There are different ways of arrangement of pins on a connector. The arrangement of pins disclosed in the above-mentioned U.S. Pat. No. 5,702,255 is shown in FIG. 3, in which the pins are arranged in multiple longitudinal and transverse rows. That is, each circle in FIG. 3 represents a position for one single pin, and each pin position has another four pin positions separately arranged at its front, rear, right, and left sides. A rate of use in one unit area provided by this type of arrangement of pins is 0.7854.
FIG. 4 shows another type of pin arrangement that is currently adopted in most conventional connectors. In this type of arrangement, pins are located on intersecting lines. That is, each pin position represented by a circle has another four pin positions spaced around it on two intersecting diagonal lines. The rate of use in one unit area provided by this type of pin arrangement is 0.7854 that is not good enough and needs improvement.
Currently, there is another LGA (Leadless Grid Array) type of connection widely adopted to connect working elements to a connector. The LGA type of connection is different from and superior to the conventional SMT and BGA types of connection in that it does not require any tin soldering. Working elements are electrically connected to the connector by forward contact with terminals in the connector. The LGA type of connection simplifies the connection in an IC structure and enables largely improved good yield of connection. Moreover, components employed in the BGA type connector can be applied to the connector adopting LGA type connection.
To achieve the LGA type connection, the working elements may have two different types of contacts, namely, a ball type contact C1 and a plane type contact C2, as illustrated in FIGS. 10A and 10B, respectively. Both the ball and the plane type contacts are connected to the terminals on the connector without using tin soldering.